Method of optimising the joints between layers in modelling or prototyping involving layer decomposition, and parts thus obtained

ABSTRACT

A method for optimizing the joints between layers in that portion thereof which is flush with the surface of a part obtained by means of computer-aided modeling or prototyping of the type involving layer decomposition, characterized in that the connecting profile of two successive layers is mathematically and numerically defined using an algorithm in which the surface of the joint ( 7 ) at the end zone close to the flush portion is always substantially normal {right arrow over (n)} to the plane tangential to the surface at the flush point.

The subject of the present invention is a method for optimizing the joints between layers in that portion thereof which is flush with the surface of a part obtained by means of computer-aided modeling or prototyping of the type involving layer decomposition.

The invention also has as its subject the elementary layers thus obtained, and the parts resulting from their assembly.

In a known method of the rapid prototyping type, the subject for example of European patent EP 0 585 502-B1, a prototype part is produced by using software for decomposing of the part to be produced into elementary layers, said layers being assembled together and then the final assembly being able to be reworked externally, particularly in order to remove any roughnesses or imperfections resulting from assembly.

FIGS. 3 and 4 show schematically a layer assembly detail with an illustration of the problem encountered.

In an assembly of two layers (1, 2), a portion of the joint (3) becomes externally flush at (4). It is understood that the zone (5) of the layer (1) comprises little material at this location, which, by machining and polishing, may result in the removal of material precisely at this joint, as shown schematically in FIG. 4 at (6).

The result of this is an imperfect part, with an irregular surface and therefore unsatisfactory for certain applications.

This conventional joint design also has other disadvantages:

-   -   poor strength;     -   poor resistance to machining;     -   poor resistance to mechanical stresses during use (in particular         compressive stresses, whether they be of mechanical or fluidic         origin);     -   poor resistance to all assembly operations: bonding, welding,         cementing;     -   possible deformations during machining, handling and during         assembly.

The object of the invention is to remedy these disadvantages.

According to the invention, the proposal in fact is a method for optimizing the joints between layers in that portion thereof which is flush with the surface of a part obtained by means of computer-aided modeling or prototyping of the type involving layer decomposition, characterized in that the connecting profile of two successive layers is mathematically and numerically defined using an algorithm in which the surface of the joint at the end zone close to the flush portion is always substantially normal to the plane tangential to the surface at the flush point.

The invention will be better understood with the aid of the description given below of a number of variant embodiments, with reference to the appended drawings in which:

FIG. 1A is a CAD representation of a part that is complicated to produce, with a few possible alternative situations,

FIG. 1B illustrates in CAD a layer obtained with the method of the invention, illustrating the latter in three dimensions,

FIGS. 2A and 2B represent a layer obtained according to the invention, seen from above (FIG. 2A) and in section (FIG. 2B),

FIGS. 3 and 4 illustrate the problems potentially encountered with the layers of the prior art,

FIGS. 5 and 6 illustrate schematically the basic principle of the method according to the invention,

FIGS. 7, 8A, 8B and 8C illustrate simple embodiment variants,

FIG. 9 illustrates an application to overhung and/or undercut profiles,

FIG. 10 illustrates a detail on a layer of an assembly according to FIG. 9,

FIG. 11 illustrates a detail on a layer of an undercut assembly according to FIG. 9, in two variants,

FIGS. 12A to F illustrate the application to a wall.

Reference is made first of all to FIG. 5.

The figure shows the essential parameters of a joint obtained according to the method of the invention:

angle α between the tangent and the layer plane,

a: length of the joint,

b: offset of the layer plane,

n

: normal at the point of junction.

According to the invention, the joint (7) is normal to the tangential plane (T) over a length a.

Note that:

if a is constant, b is f(α);

if α=π/2, b=0.

The abovementioned problem of the joint is thus solved but the layers thus obtained requiring this type of calculation will be of variable thickness.

In addition, the profile of the layer can vary all along the periphery. Also, the line of the joint is not necessarily in one and the same plane.

For angles α close to π/2, it will also be necessary to provide means of positioning the layers relative to one another, as explained below.

Refer to FIG. 6.

With all other things being equal with reference to the embodiment of FIG. 5, the following are carried out:

control of the material at the joint (the objective sought),

control of the positioning in (X,Y) by a centering insert (8),

control of the precision in (Z) by the positioning profile (8′),

control and reinforcement of the assembly and of its mechanical strength.

Various comments may be made in this regard:

the positioning profile is calculated relative to the external contour of the layer, the angle a being able to vary along this contour;

the profile may be obtained by micromilling, by milling the profile or with the aid of a form cutter. In the latter case, it is of course constant on the periphery;

the interlock is “hyperstatic”; it is possible to provide clearances therein to assist with certain contacts.

Various variants will be briefly described below:

in FIG. 7, the interlock becomes impossible to take apart due to the presence of an undercut (β) on the positioning profile (9), assembly being possible due to the elasticity of the materials;

as can be seen in FIGS. 8A, 8B and 8C, it is also possible to arrange the joint on the outside as a function of the degree of sealing required, that is to say:

-   -   to add material as a supplement, which results in an external         bead by deformation: 8B then 8C;     -   to make a joint resist, FIG. 8A.

FIGS. 9, 10 and 11 show examples of application to overhangs and undercuts.

The details on the layers in FIGS. 8 and 9 show that the decompositions are possible in overhang and undercut, still with the same joint principle, it also being possible to choose the side of the interlock (upper or lower layer) and even their combination in space.

Finally, FIGS. 12A to 12F show variants of application to the walls:

without interlock: FIG. 12A;

with external interlock only and flat: FIG. 12B;

with external and internal interlock and flat: FIG. 12C;

with external and internal interlock in the same plane: FIG. 12D;

with simple normal decomposition: FIG. 12E;

with double interlock with offset: FIG. 12F.

From the foregoing it will be noted that it is the digitization of the profile that makes it possible to obtain a mathematically defined connection and nesting profile, functionally programmed.

There is no limit, the profile being able to be warped, and the joint surfaces being able to be complex and calculated.

It will be understood that the major innovation lies in the principle of interlocking, the shapes being fully programmed and dependent on the cross-sectional area in which the nesting takes place; it may be a flat surface but also a warped surface, as shown in FIGS. 1B; 2A and 2B.

By using a geometric algorithm, the shape of the nesting joints is obtained by systematic computer calculation.

Consequently, the shape of the joint depends on the layering plane and cannot therefore be known in advance.

At the interlocks, it is possible to provide the functional portions of the induced functions in the final part, as a nonlimiting example, of the channels for regulating (cooling, heating, etc.) and/or for bringing assembly products and/or for circulation of fluids.

This method finds its application in all the fields of layered parts design by rapid prototyping and tooling already evoked, with all the possible extensions that can be imagined by those skilled in the art for the decomposition of the existing part or for the design of new parts. 

1. A method for optimizing the joints between layers in that portion thereof which is flush with the surface of a part obtained by means of computer-aided modeling or prototyping of the type involving layer decomposition, characterized in that the connecting profile of two successive layers is mathematically and numerically defined using an algorithm in which the surface of the joint (7) at the end zone close to the flush portion is always substantially normal {right arrow over (n)} to the plane tangential to the surface at the flush point.
 2. The method as claimed in claim 1, characterized in that the profile of each layer can vary all along the periphery.
 3. The method as claimed in either one of claims 1 and 2, characterized in that the interlock of two superposed layers becomes impossible to take apart due to the presence of an undercut (β) on a positioning profile (9).
 4. The method as claimed in any one of claims 1 to 3, characterized in that the joint is made with the addition of material as a supplement or joint resist.
 5. The method as claimed in any one of claims 1 to 4, characterized in that the profiles are adapted to the overhang and undercut.
 6. The method as claimed in any one of claims 1 to 5, characterized in that the positioning in (X,Y) is controlled by a centering insert (8) and that in (Z) is controlled by a positioning profile (8′).
 7. The method as claimed in any one of claims 1 to 6, characterized in that the interlock is “hyperstatic”.
 8. The method as claimed in any one of claims 1 to 7, characterized in that the angle α between the tangent T and the plane of the layer is not constant all along one and the same joint profile.
 9. An elementary layer, characterized in that it is obtained by using the method as claimed in any one of claims 1 to
 8. 10. A modeling, prototyping or tooling part, characterized in that it is obtained by the assembly of layers as claimed in claim
 9. 